Process for preparing cyclopropane



Patented Aug. 3, 1943 PROCESS FOR PREPARING CYCLOPROPANE John M. Ort,Rockvllle Centre, N. Y., assignor to E. It. Squibb & Sons, New York, N.Y., a corporation of New York No Drawing. Application October 9, 1941,Serial No. 414,355

9 Claims.

This invention relates to the preparation of cyclopropane.

Cyclopropane has heretofore been prepared by the reaction oftrimethylene dihalides with finely-divided metal reduction agents invarious liquid reaction media (in whiclthe metal is suspended and thedihalide is more or less dissolved), e. g.,, by the reaction oftrimethylene dibromide with zinc dust in aqueous ethanol. While thisprocedure has been developed to a high state of emciency, the use ofliquid reaction media gives rise to certain complications, inter alia,the (economic) necessity of recovering the medium if essentiallyalcoholic, and the occurrence of side reactions due to or involving themedium.

As described and claimed in the copending application of Christiansenand Or't, Serial No. 414,354, filed simultaneously herewith,cyclopropane can be prepared by contacting the vapor of a trimethylenedihalide with a metal reduction agent, a process which does not requirethe use of a liquid reaction medium.

The emcient operation of this process, however, requires the use 01' alarge excess of the metal reduction agent to provide the necessary fresh(active) metallic surface, and consequently requires relativelylarge-capacity equipment. If the metal reduction agent is infinely-divided form and is stirred or agitated to increase the .activesurface presented within equipment of a given capacity, some of themetal reduction agent may thereby "be carried, into the condenser.

It is the object of this invention to provide an improved process ofpreparing cyclopropane which does not require the use of a liquidreaction medium or relatively large-capacity equip ment.

The process of this invention essentially comprises intimatelycontacting a trimethylene dihalide-preferably in vapor form-with aliquid annilgam of a metal reduction agent. (The term aniaigam" is usedherein in its recognized technical sense, i. e., as designating an alloyof mercury with another metal or metals.) The intimate contact may beeffected by having the amalgam in particulate form, as by means ofvigorous stirring. The amalgam is one either liquid at room temperatureor liquefied by heating. Preferably, the metal reduction agent is usedinexcess to form an amalgam carrying (finelydivided) unamalgamated metalreduction agent.

The invention is applicable generally to the production of cyclopropaneby the reduction of trimethylene dihalides; thus, the preferredtrimethylene dihalides are the dibromide, cniorobromide, and dichloride,and the utilizable metal reduction agents include zinc, sodium, andmagnesium. The reaction is favored by operating at elevatedtemperatures, a temperature of about 200-300 C. being optimal from thestandpoint of obtaining'a reasonably rapid reaction with a minimum ofcharring.

The processis conveniently carried out as follows: The reacting vesselis fitted with a device for vigorous stirring, a reflux condenserthrough which uncondensed gas (cyclopropane) can escape to a gasometer,and a device for drop-feed. ing the trimethylene dihalide; thetemperature of the liquid amalgam is raised to well above the boilingpoint of the trimethylene dihalide used [any excess of the metalreduction agent present resting on the top of the amalgam]; the wholemetal mass (both liquid and solid, if present) is stirred vigorously, sothat particles of the liquid amalgam and finely-divided metal aredispersed throughout the interior of the reaction vessel; and thetrimethyiene dihalide is fed dropwise, whereupon it is vaporized andpart of it reacts with the metal reduction agent, the unreactedtrimethylene dihalide vapor being condensed and returned until consumed.

The following example is illustrative of the invention: 550 g. mercuryis placed in a 3-neck 3-liter flask, and 300 g. zinc dust added. Astirrer is inserted through one of the necks, a thermocouple throughanother neck, and the third neck is connected to a reflux condenser andto a device for drop-feeding the trimethylene dihalide. The flask isthen heated to 270285 C., the stirrer operated rapidly, and g. oftrimethylene dichloride is fed dropwise over a period of an hour,meanwhile collecting the evolved cyclopropane: about 40 minutesthereafter, all liquid vanishes from the reflux condenser, an thereaction is complete. An approximately yield of cyclopropane isobtained. The 300 g. zinc used is in great excess for the 60 g.trimethylene dichloride: and the excess zincand, of course, themereury-are reused after cooling, removing the reaction-formed ZnClzfrom the surface of the amalgam by washing with water, and adding morezinc dust to replace that used up in the reaction.

The use of trlmethylene chlorobromide or tri methylene dibromide in lieu01' trimethylen dichloride in the foregoing examples gives even betterresults; inasmuch as they are more reactive than the dichloride andhence do not require as high a reaction temperature, and the use oflower temperatures minimizes side reactions and increases the yield.

Magnesium or other metal reduction agents may be used in lieu of zinc inthe foreging ex-' ample; and means other than those of the foregoingexample may be used to efiect intimate contact between the trimethylenedihalide and the liquid amalgam of a metal reduction agent.

The invention may be variously otherwise embodied, within the scope ofthe appended claims.

I claim:

1. The process of preparing cyclopropane which comprises intimatelycontacting a trimethylene dihalide with a liquid amalgam of a metalreduction agent.

2. The process of preparing cyclopropane which comprises intimatelycontacting a trimethylene dihalide with a liquid amalgam of a metalreduction agent at an elevated temperature. 3. The process of preparingcyclopropane which comprises intimately contacting the vapor of atrimethylene dihalide with a liquid amalgam of a metal reduction agent.

4. The process of preparing cyclopropane which comprises intimatelycontacting the vapor of a trimethylene dihalide with a, liquid amalgamof a metal reduction agent at an elevated temperature.

5. The process or preparing cyclopropane which comprises contacting thevapor or a trimethylene dihalide with particles of a liquid amalgam of ametal reduction agent.

6. The process of preparing cyclopropane which comprises intimatelycontacting the vapor o! a trimethylene dihalide with a. liquid amalgamof a metal reduction agent, carrying unamalgamated metal reductionagent.

7. The process of preparing cyclopropane which comprises intimatelycontacting the vapor of a trimethylene dihalide with a zinc amalgam inliquid form.

8. The process of preparing cyclopropane which comprises intimatelycontacting the vapor of trimethylene dichloride with an amalgam" of ametal reduction agent in liquid form.

9. The process of preparing cyclopropane which comprises intimatelycontacting the vapor of a trimethylene dihalide with a liquid amalgam ofa metal reduction agent at a temperature of about 200-300 C.

' JOHN M. ORT.

